Unlocking one of the dozens of nondescript industrial cabinets that fill the facility’s 3,500 square feet, Sullivan reveals drawer after drawer containing birds, mice, squirrels, insects, reptiles and other creatures.

Each specimen — from beetles smaller than a pinhead to massive condors — is tagged with information revealing the date it was collected and the location where it was found.

A single bird captured north of the Arctic Circle in Barrow, Alaska, in the 1920s can offer a wealth of information about life a century ago, Sullivan said.

If there are terns, that means there are fish. If there are fish, that means there is plankton. If there's plankton, that means a low incidence of pesticides, said Sullivan, who vastly prefers this tangible and more tactile form of scientific inquiry to the comparatively sterile field of genetics — "a bunch of clear fluids you're moving from bucket to bucket."

The value of having dozens of samples of the same species collected over decades, he explained, is that scientists can detect changes over time in traits like beak length, wing span and length of body.

Sullivan, who's been with the museum for 11 years, recalled one researcher who examined specimens of mice from before and after the city of Chicago was founded.

“The body shape had changed, the skulls were flatter,” he said. “Simply by building a city, we could change the genetics of the common mouse.”

The Chicago Academy of Sciences, which moved to the Notebeart museum when it opened in 1999, was founded in 1857 at the height of the Victorian Era’s budding interest in scientific exploration. Its collection was built in part by amateur naturalists who traveled to the then far-flung locales of Alaska and Florida, bringing back specimens of previously unknown species.

“It was how you spent your leisure time,” said Sullivan, who has a degree in zoology and is working toward a Ph.D. in ecology and evolution. "It was the golden age of discovering diversity."

In maintaining the specimens as a “public trust,” the museum’s purpose is two-fold, he said. One is to preserve the samples as long as possible by isolating them from agents of deterioration (hence the pervasive smell of naphthalene, aka moth balls, and no, he said, you never get used to it). The other is to make the specimens as accessible as possible.

Outreach includes opening up the facility to public tours during the Ravenswood Art Walk in October, as well as research efforts that engage the public, like Project Squirrel, a scientific study led by Sullivan. The center is open to researchers and school groups, too.

"It's a way for people to look in their own back yard," he said.

The project asks participants to log their observations. "If they see squirrels, report it. If they don't see squirrels, report it."

In connecting individuals to their environment, the museum aims to promote a greater understanding among humans of the plant and animal life around them.

To illustrate his point, Sullivan opens up a cabinet containing some of his favorite specimens, Passenger Pigeons, which have been extinct since the last one died in a Cincinnati zoo in 1914.

Sullivan reverently holds up one of the pigeons, known in their day as the Blue Meteor for their ability to reach speeds of 60 miles per hour.

"They used to be able to blanket the sky like twilight," he said. Once numbering in the billions, flocks of the migrating birds took three days to pass over an area.

Chicago was a trading center for the pigeons, which were slaughtered for their meat, said Sullivan.

"Within 50 years, we killed every last one" through hunting and habitat encroachment, he said. "This is a story about humans and human interaction. We need to create more sustainable interactions with the natural world."

More than just some quaint relic from the past, the museum's collection of Passenger Pigeons informs current study.

The birds represent a cautionary tale that's continuing to play out in places like Java, he said, where humans' demand for coffee caused the extinction of the Javan tiger, and Borneo, where our desire for palm oil is threatening the habitat of orangutans.

The role of the Nature Museum, he said, is to support ecological principals, creating links between individual behavior and broader issues, particularly among urbanites for whom "wilderness" seems like a foreign concept.

"So Borneo becomes our back yard," said Sullivan. "We're all making impacts. The museum can show you how to get out into the wild, or make decisions that impact the wild."

He pointed to the museum's current "Food" exhibit, which demonstrates the way humans' food choices affect the environment.

"We are not a frontier people anymore, we're not connected to wildlife, but our impacts are still being felt by those areas," he said.

For Chicagoans, getting back in touch with our naturalist roots doesn't require anything more than stepping out the front door, said Sullivan.